Astronomy

2016-2017: Jupiter’s Year With Spica, A Triple Conjunction

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This appearance of Jupiter has ended.  See this article for the next apparition:

2017-2018:  Jupiter’s Year in the Claws of the Scorpion, A Triple Conjunction

Figure 1: Jupiter’s Morning Appearance in Late 2015 with Venus and Mars

In late September 2016, Jupiter begins a 396-day appearance that includes a triple conjunction with the star Spica.  A triple conjunction occurs when a planet appears to pass a star or another planet three times during a single appearance.  There are multiple definitions of a conjunction:  The simplest is the closest separation between a planet and another celestial object.  Two others are based on coordinate systems:  the solar system plane (ecliptic) and the plane of the earth’s equator (equatorial).  Coordinate systems have specific names for longitude and latitude.  In these systems conjunctions occur when the star’s longitude is the same the planet’s changing longitude as it revolves around the sun.  One could say that an airplane flying across the country is in conjunction with a city when its longitude matches the city’s longitude.  For our purposes a star’s celestial coordinates are constant while the planet’s coordinates change as it revolves around the sun.

The celestial equator and ecliptic

Since the ecliptic is angled with the celestial equator by 23.5 degrees, a planet’s ecliptic longitude and equatorial longitude are not the same.  For this article, the triple conjunction occurs in the equatorial coordinate system.

Jupiter begins its morning appearance on September 26, 2016, nearly a month after its Epoch Conjunction with Venus.  On this date, Jupiter is  behind the sun in solar conjunction.

Jupiter completes one solar orbit about every 11 earth years.  Because Jupiter slowly lumbers through its orbital path, it does not travel far among the stars during the earth’s annual path around the sun.

Figure 2:  Jupiter at conjunction

The chart above shows the positions of Earth and Jupiter with the sun in between (conjunction).  The sun’s bright glare blocks us from viewing Jupiter.

Figure 3:  Jupiter rising in the morning sky

Jupiter then begins its appearance in the morning sky, initially rising during twilight.  By mid-October, it rises about an hour before sunrise.  The chart above shows the rising times of Jupiter, the star Spica, Mercury, and the moon (circles) compared to sunrise. (As the moon heads towards its new phase, it rises later each morning.) The astronomical twilight line represents the time when the sky is as dark as it every gets naturally.  As the sky brightens, the ground can be discerned from the sky:  Nautical twilight.  So named because at sea the horizon clearly separates the water from the sky.  At Civil Twilight, the sky is bright, most details of terrestrial features can be identified.  Street lights normally turn off during the time between Civil Twilight and sunrise (or turn on during evening Civil Twilight).

Jupiter rises earlier each day, appearing higher in the eastern sky as sunrise approaches.  On October 11, the Mercury and Jupiter line cross, indicating that they rise at the same time.

 

Figure 4:  Jupiter and Mercury, October 11, 2016

On this date, Mercury passes less than one degree from Jupiter.  This chart shows them about 30 minutes before sunrise.  Binoculars may be needed to locate Mercury in the brightening twilight before sunrise.  Locate a clear eastern horizon as the pair is just 5 degrees above the horizon. (See this article for more details of Mercury’s morning appearance.)

Figure 5:  The moon and Jupiter’s closest approach to Gamma Virginis

By late October, Jupiter rises at the beginning of astronomical twilight and by year’s end it rises over 5 hours before sunrise.  Notice that on October 28, Jupiter and the moon rise at nearly the same time.  Jupiter’s closest approach to the star Gamma Virginis is on this morning, but the planet passes this star two mornings later in the equatorial system.

Figure 6:  Jupiter’s retrograde & Spica Conjunctions

Movie 1:  This video explains the chart above.

Jupiter’s westward march with the stars is from the earth’s orbit around the sun.  The Giant Planet appears to move against the starry background as well; this is from the planet’s orbital progression and the faster earth’s orbit around the sun.  On the diagram (Figure 6) above, Jupiter is shown beginning October 28, 2016, when is rises over 2 hours before the sun with each yellow dot representing a day.  The planet moves noticeably eastward in the general direction of the bright star Spica.

Figure 7:  October 28, Jupiter and the star Spica are separated by 14 degrees

This chart shows Jupiter and Spica on October 28, 2016, date on that Jupiter is enters the retrograde chart in the previous chart (Figure 6).  Jupiter appears low in the predawn eastern sky before sunrise with a waning crescent moon.  Spica is 14 degrees below Jupiter near the horizon.  (This is the same morning that Jupiter is closest to Gamma Virginis.  See Figure 5.)

Figure 8:  Jupiter and Spica:  November 15, 2016

By mid-November, Jupiter rises over 3 hours before the sun.  The star Spica appears about 10 degrees below Jupiter.  From the the sunrise chart (Figure 3) above, notice that the time between rising times for Jupiter and Spica narrows throughout 2016.  Jupiter appears to move farther east compared to that starry background (see Figure 6).

Figure 9:  December 31, Jupiter and Spica are 4 degrees apart.

By year’s end, Jupiter appears to move eastward until it is about 4 degrees above Spica. Jupiter is slowing in its apparent eastward movement (See Figure 6), although it does not slow in its orbital motion.

Figure 10:  January 11, 2017, Jupiter appears 90 degrees from the sun

As the weeks pass, Jupiter rises earlier each morning from the Earth’s revolution around the sun.  On January 11, Jupiter appears 90 degrees west of the sun, meaning that it rises around midnight and by sunrise it is in the south.

Figure 11:  January 20, the first conjunction of Jupiter and Spica

Jupiter passes Spica the first time on January 20, 2017 when they are about 3.5 degrees apart.  Jupiter appears to slow its eastward movement, but its orbital speed stays the same.

Figure 12:  February 9, 2017, Jupiter appears to be stationary.

Compared to the background of stars, Jupiter appears to stop its eastward motion on February 9, 2017 (See Figure 6), and appears to begin to move backward (west or retrograde) compared to the stars.

Figure 13:  February 23,  Jupiter’s second conjunction with Spica.

As Jupiter retrogrades, it passes Spica again on February 23, by a margin of nearly 4 degrees.

Figure 14:  April 7, 2017:  Jupiter is at opposition

This apparent westward motion is continues until June 8, 2017.  On April 7, Earth moves between the sun and Jupiter as shown above ( Also see Figure 6).  This is known as opposition; that is, Jupiter and the sun are on opposite sides of our planet and appear on opposite sides of the sky.  When the sun sets in the west, Jupiter rises in the east.  As Earth rotates, Jupiter appears south at midnight and by sunrise Jupiter is in the western sky near the horizon as sunrise approaches in the eastern sky.

Figure 15:  April 7, 2017, Jupiter at opposition with Spica nearby

As shown in this diagram, Jupiter and Spica appear in the early evening sky on opposition night.

Figure 16:  June 8, 2017, Jupiter stops retrograding

Jupiter continues to retrograde and appearing farther west each evening as compared to Spica (See Figure 6).  On June 8, 2017, Jupiter stops retrograding and again appears to move to the eastward against the sidereal background.  The eastward progress is small at first glance, then Jupiter’s eastward motion is easily observed.

Figure 17:  The western evening sky at.  This chart shows the stars, planets, and the moon setting times compared to sunset from June 15, 2017 to November 2, 2017.

Jupiter sets earlier each evening as shown in this chart which shows the objects setting times relative to sunset.  Notice the proximity of the Jupiter setting line and the Spica setting line.  Before early August 2017, Jupiter sets before Spica.  After that date it sets after Spica.  Other diagrams in this article show their relative positions in the sky,  The moon setting time is indicated by the circles.

Earth’s faster speed carries it past Jupiter and by July 5, 2017, Jupiter appears 90 degrees east of the sun, visible in the southern sky at sunset.  This is nearly a month after Jupiter appears to resume its eastward motion compared to the stars and the stellar signpost Spica.

As Jupiter and Spica disappear into the sun’s glare as Jupiter heads for another solar conjunction (October 27, 2017), this solar system giant, appears to pass Spica again (3.3 degrees) for the third conjunction of this apparition — a triple conjunction.

Jupiter’s track leaves the retrograde diagram (Figure 6), on September 12, 2017 after 337 days of chronicling the planet’s apparent movement against the stellar background.

The earth’s orbital speed carries Jupiter behind the sun to solar conjunction only for Jupiter to reappear in the morning sky in 2017.  Jupiter is headed for a December 21, 2020 conjunction with Saturn when the pair appear 0.1 degree apart.  Meanwhile the next Venus-Jupiter conjunction is November 13, 2017 — another Epoch (close) conjunction of those planets during bright morning twilight.

Appearances with the Moon

Morning dates, visible before sunrise, when Moon appears near Jupiter.  Bookmark this page to see photographs of the groupings, weather permitting.

  • October 28, 2016

  • November 24 & 25, 2016
  • December 22, 2016
  • January 19, 2017
  • February 15, 2017  (Look late in the evening as well)
  • March 14 & 15, 2017 (Late pm as well.)

Evening dates

  • April 10, 2017
  • May 7, 2017
  • June 3, 2017
  • June 30 & July 1, 2017
  • July 28 & 29, 2017
  • August 24 & 25, 2017
  • September 21, 2017

Our images and charts collections are available here –> http://goo.gl/Sfp1ur

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